Diseases in plants may be caused by environmental factors or by living organisms. Environmental factors such as drought, excessive moisture, lack of nutrition, improper temperature, etc., are generally controlled by proper management techniques, while disease-causing organisms such as fungi and bacteria may be somewhat more difficult to control. There are literally thousands of such organisms, and they may inhabit and infect the soil or roots, as well as the visible plant. Because of the significant economic roles of both nutritive and decorative plants, the effective treatment of plant diseases caused by fungal and other organisms is an important goal which has long demanded considerable attention.
A variety of agents are known to control diseases in plants. For example, copper-containing and lime-sulfur sprays have been used to control fungus and bacterial diseases, particularly on fruit trees, berry bushes and roses. Similarly, bleaches and other chlorine-based compounds have been used in certain circumstances, although somewhat less commonly as their harmful side effects have become more fully appreciated. Also, organic fungicides such as Captan (N-trichloromethylthio tetrahydrophthalimide), Arasan (tetramethyl-thiuram disulfide), Semesan (hydroxmercurichlorophenol) and Spergon (tetrachlorobenxoquinone) have been used with limited success.
Many of the products available for plant disease control have substantial limitations. For example, treatment with copper is generally not preferred, in part due to its phytotoxicity. Also, many agents provide an unsatisfactory spectrum of activity due to the resistance which develops in the target pathogens. In addition, some potential disease control agents are effective only in a narrow pH range, and are therefore not suitable for general agricultural use. Finally, some prior art agents, such as bleach or various quaternary ammonium compounds, are toxic not only to the target pathogen, but to humans and animals as well.
In addition to health hazards from the toxicity of the disease control agents of the prior art, such agents also typically involve other dangers such as explosiveness, corrosivity, etc. Also, conventional chlorine-based compounds exhibit instability in the presence of organic matter, and tend to form chloramines in the presence of ammonia--thereby producing residual compounds which undesirably persist in the environment.
A need therefore exists for improved methods and agents for the control of diseases in plants. In particular, a need exists for agents which provide effective control of diseases in plants without being toxic to either the plant or the consumer of the plant or its fruit. A need further exists for agents which may be used to treat plant seeds to ward off diseases which may infest the seeds. The present invention addresses these needs.